Which Came First?

A man was helping one of his cows deliver her calf, when he noticed his 4 year-old son standing wide-eyed at the fence, soaking in the whole event.
The young father thought, "Great... he's 4 and I'm gonna have to start explaining the birds and bees. No need to jump in too deep... Let him ask a question, and I'll answer."
After everything was over, the man walked over to his son and said, "Well little buddy, do you have any questions?"
"Just one, Daddy!" gasped the still wide-eyed boy. "How fast was that calf going when he hit the cow?"
Originally published November 14, 2002.